This proposal describes a 5-year training program for the development of an academic career in the clinical pharmacology of arrhythmias. This program is designed to expand the laboratory-based skills of a clinical scientist that will result in a translational research program focused on arrhythmogenesis. Heart failure can be broadly characterized by a sympathetic hyperactivity and is associated with an increased risk for the development of atrial fibrillation. The slow component of the delayed rectifier current, IKs, is regulated by acute adrenergic receptor-mediated phosphorylation but its functional status and regulation during heart failure are unknown. Alterations of IKs function during heart failure could have therapeutic implications since the enhanced function of this current has been associated with the generation of atrial fibrillation. The central hypothesis for this application is that; sustained adrenergic-receptor activation contributes to an atrial arrhythmogenic substrate via lasting alterations in the regulation of the phosphorylation status, and hence function of IKs. We propose a systematic series of investigations to assess pathological alterations in the regulation of IKs and mechanisms of atrial arrhythmias in an experimental model of sustained adrenergic receptor activation. Specific Aim 1 will test the functionality, regulation, and phosphorylation status of the proteins underlying IKs following sustained adrenergic receptor stimulation. Specific Aim 2 will test electrophysiological mechanisms for atrial arrhythmogenesis during left ventricular dysfunction by assessing the interplay of focal triggers and reentrant mechanisms. Overall, this research sequence corresponds directly to the proposed training program that has been designed to impact a clinical problem while setting the foundation for a career in translational research. This will lead to a translational research program combining mechanistic studies with clinical research to rationally develop effective preventative strategies for atrial fibrillation in patients at the highest risk to develop the arrhythmia.